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Tuesday, 28 December 2010

Tech Analysis: Mass Effect 2 Demo (PS3 vs 360)

This year we have already seen a tangible improvement in PS3 games that use the Unreal Engine 3, or even the UE in general. While titles such as Bioshock 2 added fire to the flames with low resolution alpha buffers and the inclusion of blur a filter of sorts, titles such as Ninja Theory’s Enslaved and the Activision published Singularity, showed that when optimised, PS3 versions of UE3 games could look and indeed run almost identically, with performance being the main separating factor.

The engine powering Mass Effect 2 on the PS3 is basically an updated, highly customised version of the UE3, an engine which is largely tailored to the Xbox 360 and its high levels of memory bandwidth delivering usually solid performance and plenty of full resolution visual effects. It's not uncommon then, to see the PS3 often struggling to cope with displaying the same level of visual fidelity given the engine’s use of high resolution alpha, and large instances of normal mapped transparencies.

However, as we’ve seen in two titles which use the engine this year, platform parity is indeed possible with some careful optimisations, and this is exactly what Bioware have done when approaching the PS3 version of Mass Effect 2. There are of course a few mandatory cutbacks, where the PS3’s reduced memory bandwidth automatically means a small hit in certain graphical effects and shaders, but there are also a few improvements too, not least of all more natural use of lighting and better overall performance.

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PS3

Starting off with a look at the framebuffer, Mass Effect 2 renders in 720p (1280x720) on both platforms with what appears to be no anti-aliasing. However, as we’ve discussed before, the way the Unreal Engine 3 works means that standard MSAA solutions are often broken, with most edges simply getting zero AA at all. And this is exactly what we find here.

ME2 does in fact feature 2xMSAA on 360 in its core rendering make-up, although, due to the differed nature of how the UE engine operates in ME2 – rendering various parts of the framebuffer in different passes – the effect is basically borked to the extent of not being there at all. Once all elements have been added in rendering the final frame, we are left with a image devoid of any kind of noticeable edge smoothing. While on the other hand, the PS3 version seems to feature no AA at all.

Aliasing and shimmering then is often noticeable in high contrast areas, although overall IQ improves a little in dark scenes whereby distinct edges are less apparent. Both PS3 and 360 builds are basically identical in this regard.

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PS3

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PS3

Outside of the FB, Mass Effect 2 features both some obvious, and not so obvious upgrades and downgrades to the game engine on the PS3. As expected, allowances have had to be made for the console’s reduced memory bandwidth compared to the 360. As we’ve discussed many times before, with no EDRAM there is less bandwidth for normal mapping, textures, and shader effects, all of which have an impact on how the engine must be tailored to work around these limitations.

Here, we see that the PS3 version of the game features lower resolution/less detailed texturing on characters faces, along with paired back shader effects. Notice how subtle details, such as pores, fine lines etc, appear flatter and less pronounced on the PS3, and the skin in general having a slightly less detailed look to it. This tends to be more noticeable in some scenes than others, with lighting, shadowing, and camera distance all playing a part.

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PS3

Another area in which the PS3 build sees similar changes in rendering quality, is with regards to normal mapping and specular highlighting. In addition to the paired back nature of texturing and shader effects on characters, we can see what looks like lower resolution normal mapping and downgraded specular on the characters.

In terms of specular, in some scenes use of the effect is simply rendered differently – apparent on character faces - but in a similar resolution to that of the 360 game, while in others the effect actually seems to be either completely absent or rendered in a lower res.

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PS3

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PS3

We can also see a reduction/lack of specular reflections in some parts of the environment itself, caused by the absence of any HDR-like bloom lighting on the PS3. The metal frame around the glass has what looks like both a specular and diffuse reflection map on the 360 game, whereas on the PS3 only what looks like the diffuse effect seems to be present.

Another example can be see in the second row of screenshots above, in a scene in which the difference is more apparent in the 360 game. The scene’s lighting composition makes the effect look a tad more intense, with shiny objects providing ample reflections. By contrast, on the PS3 the level of sheen and reflective properties has been paired back in comparison.

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PS3

Interestingly, Bioware have for some elements of the game seemed to have upped the texture resolution of certain details on character clothing in direct compromise to removing the use of normal mapping. Above we can see that Miranda’s hexagonal suit uses a higher res texture map on the PS3, but at the same time isn’t normal mapped at all.

Arguably, the choice in using slightly higher resolution assets in it self would use up more memory than preserving it – which again isn’t an ideal solution when working on PS3. However, the cost of normal mapping in this case is indeed greater than that of a higher res texture, so by compromising in this way the developers still make the required savings in memory while also reducing the overall discrepancy between both builds.

In which case, Bioware has clearly made the right choice. The lack of normals doesn’t impact greatly on the scene in general, with lighting and shadowing still bringing depth to it. Occasionally, there are times whereby things do appear to look a little flatter as a result of this change, but nothing remotely impactfull. The characters still look great.

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PS3

Moving on, and we can see that Bioware have made most of the downgrades on the characters themselves - with the exception of the removal of bloom and specular, the environments are largely left untouched looking exactly the same as found in the 360 version. From what I gather, it stands to reason that it was far easier for the team to make cuts on elements which are constantly present throughout the entire game – the characters - rather than having to shift through all the environment modelling downgrading parts from there.

However, beyond this there have also been a number of improvements to the engine powering Mass Effect 2 on the PS3. Being crafted from the newer, massively customised version of the UE3 – used in the upcoming ME3 - there have been a small range of upgrades and changes to both lighting and shadow composition along with performance compared to the 360 build of the game.

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PS3

The first of these improvements on the PS3 version of the game comes with a differing approach to shadow filtering more suited to the Sony platform. On the 360, ME2 used jittered samples for filtering of its shadowmaps, thus leaving an unsightly dithered look to shadow edges. By contrast, on PS3 the developers have implemented the standard PCF shadowmap filtering that comes as standard – and with next to no cost –in order to improve shadow edges.

As a result we can see cleaner, sharper shadow edges on the PS3 build. The actual resolution of the shadowmaps themselves are still low resolution on both, it’s just the use of filtering that has changed. Obviously, the PCF method still results in some jittering shadows, like in Gran Turismo 5, which is unfortuniteky unavoidable, although preferable to the dithery shadows on the 360 game.

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PS3

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PS3

The second change is with regards to the overall lighting system implemented throughout the game. While the use of bloom has been removed from the PS3 engine code, the game features a more natural looking lighting system as a whole, with increased environmental and character shadow details, along with less harsh lighting from various specific lightsources.

Lighting appears to be more ambient in nature, and doesn’t suffer from intensely lighting up character faces like if they were to have a direct light source shining on them. Sometimes this makes it look like the characters aren’t being lit up by specific environment lights, though often it makes the scene look less contrasty and easier on the eyes.

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PS3

Not all the changes in the lighting scheme work quite as well though, with various errors in lighting taking place – no doubt owing to the use of the ME3 lighting engine, and converting the ME2 lighting over to it for the PS3 build. Occasionally we see characters that aren’t lit and shaded as they as supposed to be, covered in darkness with ambient light barely having any impact.

Also, the use of self-shadowing in the PS3 build can also appear somewhat strong, sometimes looking a tad overdone in comparison to the implementation of the effect on the 360.

However, these oddities largely don’t take away anything from the modified lighting solution, with the lack of strong, often harsh source-dependant lights creating a slightly more balanced tone to things overall. Clearly, Bioware have had to make a compromise in fitting the lighting scheme from ME2 into something that would work in the new engine, and as a result some errors are inevitable, which is something that could only be sorted out with a complete re-write of the way lighting is handled as a whole in ME2. But given both time constraints and the impending release of ME3, that wasn’t at all feasible.

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PS3

Lastly, in terms of performance we see that both versions have been optimised in different ways, with separate approaches to maintaining framerate and enabling v-sync. Now, while we can only compare the first part of the demo - the 360 one features a different second scenario - it is clear that performance is reasonably good on both platforms during gameplay, but on the whole seems to be better on the PS3 (both game play and cut-scenes), with less in the way of framerate drops at the expense of noticeable screen tearing.

Essentially, the 360 build is continuously v-synced, with screen tear only visible within the overscan area of the screen. As the load increases so the engine struggles to cope, and we see a drop in framerate down from the targeted 30fps down to something approaching the 20fps mark and then back up again. This is most noticeable during the cut-scenes, as during the opening gameplay section the framerate comes close to consitantly running at 30fps. Although, the framerate can drop down slightly more in some places on the PS3 compared to the 360, along with also spiking up beyond the 30fps mark.

By contrast, the PS3 build runs with an uncapped framerate and intermittent use of v-sync, whereby as the framerate begins to drop below the 30fps mark the engine ditches sync in order to keep a steady update throughout. The upside: is that we see a far more consistent 30fps update in the PS3 build overall, with framerates still dropping in heavier load scenarios. The downside: is that the game suffers from noticeable screen tearing.

So, the game’s cut-scenes run much smoother on the PS3, but drop frames noticeably on the 360. Tearing however, like during actual gameplay is visible as a result. In addition, the use of an uncapped framerate sometimes creates an uneven screen refresh experience during gameplay, whereby a constant upping and dropping of frames can create a few jerky moments in areas with little detail or that don’t greatly tax the engine.

But all in all, both versions seem to be well optimised for the platforms they are running on. All things considered, Bioware have differing priorities when attempting to deliver stable performance on each console, with the 360 game favouring a lower average framerate over tearing frames, and the PS3 build benefiting by running smoother, tearing frames when the engine isn’t ready to render the next one.

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In conclusion, with Mass Effect 2 Bioware definitely looks to be on track in delivering a solid conversion of the game to the PS3, boasting some subtle and noticeable engine improvements, but with a few obviously inevitable downgrades. However, the cuts made in facial texture details, specular effects, and shaders barely impact on the overall experience as a whole. The PS3 version also benefits from having a more natural lighting scheme, which is easier on the eyes in scenes with high contrast lighting, and performance is for the most part - sans tearing - better than on 360.

Some rendering errors, like the odd instances of what looks like a failure to light characters in certain scenes properly, or the reduced levels of effects, due to PS3’s memory constraints, mean that neither version comes out on top – technically speaking, it can often feel like being tit for tat. But ultimately, both fare excellently in this regard anyway, featuring plenty of detail and a mostly balanced use of shadowing, which means that some of the choices will come down to which overall look you prefer than raw technical merit.

Obviously, the demo provides us with only a sample teaser of how both versions compare. But from both the opening segment and the second section exclusive to the PS3 demo, I’d be more than happy to go with the Sony version given the choice, especially as the final game will include all of the DLC and extra content of the 360 original. But either way on the very basis of the game itself, Mass Effect 2 should be well worth picking up whichever platform you happen to own.

Thanks go out to Mazinger Dude for the screens, and of course as ever to AlStrong for counting those pixels.

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